In order for an imaging medium to be widely accepted by consumers for imaging applications, such as photographic prints, it has to meet requirements for preferred basis weight, caliper, stiffness, smoothness, gloss, whiteness, and opacity. Imaging media with properties outside the typical range for ‘imaging media’ suffer low consumer acceptance.
It is important, therefore, for an imaging medium to simultaneously satisfy several requirements. One commonly used technique for simultaneously satisfying multiple requirements is to use composite structures, wherein each layer or the structure, individually or synergistically, serves one or more functions. To form a composite or layered structure, multiple operations are required in order to manufacture each layer and assemble all of the individual layers into a single imaging medium.
Imaging media typically include at least a base or support layer, and an imaging layer. The support can include raw paper base, polymeric materials, or both. One type of imaging layer is an image receiving layer. The image receiver elements known in the art require at least an image receiving layer and a support, at least one of which is porous or non-porous, that is, swellable. See, for example U.S. Pat. Publ. No. 2007/0003713 at [0026]-[0027]; U.S. Pat. Publ. No. 2005/0191444; U.S. Pat. Publ. No. 2007/0054070. The imaging layer typically comprises one or more polymeric material, and may include additional additives, such as colorants, brighteners, antistatic agents, anticurl agents, or slip agents or lubricants. Imaging media can also include cushioning layers, adhesive layers, slip layers, anticurl layers, antistat layers, or other functional layers as needed, depending on the type of imaging operation.
The inclusion of multiple different layers of different materials requires multiple materials, multiple manufacturing steps, identification of materials that adhere sufficiently or use of adhesive layers, and inhibits recycling efforts. Furthermore addition of multiple layers to carry out different functions in an image receiver introduces different failure interfaces during finishing (U.S. Pat. Nos. 7,143,674 and 7,179,523). The inclusion of multiple different layers of different materials also reduces the ability to recycle imaging media. Current media cannot easily be recycled because they are typically composites of raw paper base and polymeric materials, and cannot be recycled using standard polymer recovery processes or paper recovery processes.
To reduce the number of layers in an imaging medium, polymer foams or voided polymers can be used. These material can be referred to as “voided,” “foamed,” “cellular,” or “expanded” polymers or plastics.
There are many examples of voided receiving layers. For example, U.S. Pat. No. 5,084,334 discloses a voided polyester film having a non-compatible blend of polyester resins in which voids are formed around fine particles. Particles sizes are dispersed in a manner that provides a concentration of finer particle near the surfaces and a larger particle size near the central part of the polyester core in order to provide a different amount of voiding at the surface as opposed to the core when biaxially stretched. The film can be used in forming labels. U.S. Pat. No. 6,379,780 to Laney et al., U.S. Pat. Nos. 6,489,008, and 6,409,334 to Campbell et al. disclose an inkjet recording element comprising an ink-permeable polyester substrate comprising a base polyester layer and an ink-permeable upper polyester layer, the upper polyester layer comprising a continuous polyester phase having an ink absorbency rate resulting in a dry time of less than about 10 seconds and a total absorbent capacity of at least about 14 cc/m2, the substrate having thereon a porous image-receiving layer having interconnecting voids. U.S. Pat. No. 5,443,780 to Matsumoto et al. discloses the use of an oriented film of polylactic acid and methods for producing the same. U.S. Pat. No. 5,405,887 to Morita et al. discloses breathable, hydrolysable, porous films made by a process comprising adding finely powdered filler having an average particle size of 0.3 to 4 μm to a polylactic acid based resin. Such films are described as useful as a material for leak proof films of sanitary materials and packaging materials. Such materials are, therefore, not open-pore in nature. Commonly assigned U.S. Pat. No. 7,074,465 to Campbell et al., hereby incorporated by reference in its entirety, disclose an inkjet recording element comprising a porous ink-receiving layer over and adjacent to an ink-permeable microvoided substrate layer comprising a polyester ionomer, said substrate layer comprising 5 to 70 percent by weight solids of a neutral polyester; 5 to 40 percent by weight solids of a polyester ionomer; and 25 to 65 percent by weight of a voiding agent, wherein the microvoided substrate layer and the porous ink-receiving microvoided layer both having interconnecting voids. In one preferred embodiment of the invention, the ink-permeable polyester microvoided substrate layer comprises sulfonated polyester and the ink-permeable microvoided layer comprising a continuous phase is a polylactic-acid-based material. U.S. Pat. Publ. No. 2005/0112302 discloses an inkjet recording element comprises a permeable microvoided polylactic-acid-containing layer having interconnecting voids. The invention is also directed to method of using such recording elements in an inkjet printing process and to sheets useful for making such inkjet recording elements and other media. U.S. Pat. Publ. No. 2007/0054070 discloses an inkjet recording element comprising a support extrusion coated with a porous hydrophilic material. The porous hydrophilic receiving layer may be applied over a microvoided polylactic-acid-containing base layer containing interconnected voids to efficiently absorb the printed inks commonly applied to ink-jet imaging supports without the need of multiple processing steps and multiple coated layers. U.S. Pat. No. 7,078,367 discloses a thermal dye-transfer dye-image receiving element comprising a thermal dye-transfer receiver element comprising a dye-receiving layer on a microvoided substrate layer containing a polylactic-acid-based material and an optional support layer. In order for the polylactic acid layer to receive imaging material, the microvoids are interconnected. Col. 7, lines 35-45. U.S. Pat. Publ. No. 2005/0112351 discloses a reflective optical film comprising a layer containing a polylactic acid voided with inorganic particles in a size and an amount sufficient to provide a visible light reflectivity of at least 96%. [0076] discloses an absorbent dye receiving layer. JP 2001-213058A and JP 2001-138644A disclose use of an image receiving layer having hollow particles on a base layer. U.S. Pat. Nos. 6,863,939, 6,703,193 and 6,867,168 relate to imaging elements comprising a microvoided layer comprising a continuous phase polyester matrix having dispersed therein crosslinked organic microbeads and non-crosslinked polymer particles that are immiscible with the polyester matrix of said microvoided layer. U.S. Pat. Publ. No. 2006/0204685 and 2006/0204686 disclose an inkjet recording element comprising, from top to bottom, a fusible, porous layer comprising a mixture of fusible reactive polymer particles that comprise a thermoplastic polymer, with at least two reactive functional groups on two different particles in the mixture are capable of crosslinking with each other in the different particles on a support. Optionally, an ink-carrier-liquid receptive layer is present between the fusible, porous layer and the support. The support may include polylactic acid polymer. U.S. Pat. No. 7,198,363 discloses an inkjet recording element having a support bearing a fusible, porous layers of fusible polymeric particles and binder. U.S. Pat. Publ. No. 2007/0003713 discloses a method of printing on an inkjet recording element. The element is formed by a support having thereon in order: a) a porous upper fusible layer of fusible polymeric materials and a binder, b) a porous ink-receiving layer in which pigmented ink is stratified such that, after fusing the printed element, greater than 50% of the printed pigment colorant particles in the inkjet ink composition is retained in the bottom half of the upper porous fusible layer. One polymer used in the porous support is polylactic acid (PLA). [0026-27][0066-67]
There are many examples of voided intermediate layers. U.S. Pat. Publ. Nos. US 2005/0187104 A1, US 2005/0187105 A1, and US 2005/0187106 A1 are directed to thermal dye-transfer imaging elements, such as labels, having a polylactic acid microvoided intermediate layer with a dye-receiving layer on one side, and an optional substrate on the opposite side of the microvoided layer. U.S. Pat. Publ. No. 2006/0204684 discloses an inkjet recording element comprising a support having thereon in order, from top to bottom, a fusible, porous layer comprising fusible multifunctional polymer particles derived from an aqueous dispersion that comprise a thermoplastic polymer with at least two reactive functional groups capable of crosslinking with each other. The element contains a microvoided layer with interconnecting pores, which starts porous, then becomes a fused, continuous, image-containing layer [0076] on a separate support. [0094] U.S. Pat. Publ. No. 2007/0031615 relates to a printing media comprising a first side comprising a first exposed layer comprising a mixture of polyolefin and at least one member selected from the group consisting of polyolefin copolymers, amide containing polymers, and ester containing polymers, wherein a measured Tg of said exposed layer comprises a Tg of less than 5 degrees C. and a second side comprising an a second exposed layer having an advancing contact angle with water of less than 90 degrees. The media may include a polylactic acid polymer (PLA).
There are many examples of foamed receiving elements. U.S. Pat. Appl. Publ. Nos. US 2005/0181196 A1 and 2005/0191569 A1, and U.S. Pat. Nos. 6,447,976 B1, 6,514,659, and 6,787,217 B2, all disclose imaging elements having a closed-cell foam core and at least one flange layer adjacent the foam core. In each case, an image receiving layer is placed on the opposite side of the flange layer from the foam core. U.S. Pat. Nos. 6,566,033, 6,537,656, 6,447,976, and U.S. Pat. Publ. Nos. 2003/0219663 A1 and 2003/0152760 A1 also describe foam core elements for use in imaging applications. U.S. Pat. Publ. No. US 2004/0229966 A1 and U.S. Pat. No. 6,958,365 are directed to open celled microcellular foam which can be used as the image-receiving layer in a structure comprising a support, an absorbing layer on the support, and the image-receiving layer on the absorbing layer. U.S. Pat. Publ. No. 2004/0119189 relates to a method for placing indicia on a flanged, closed cell foam support for an imaging element, wherein the imaging element comprises the support and at least one imaging layer. The invention also relates to a method for placing indicia on a support for an imaging element comprising providing a support wherein the support comprises a closed cell foam core layer and adhered thereto at least one flange layer, wherein the closed cell foam core layer comprises a polymer that has been expanded through the use of a blowing agent, and placing indicia on the closed cell foam core layer.
U.S. Pat. Publ. No. 2004/0258857 relates to an imaging element having long term stability comprising at least one imaging layer and a support. The support comprises at least one layer comprising polylactic acid (PLA). The imaging support and imaging layers are separate layers. U.S. Pat. Nos. 7,094,733 and 7,078,368 disclose thermal-dye-transfer labels, and pre-label media from which they are made, comprise a dye receiving layer on an extruded pragmatic polymer film comprising a microvoided layer, a continuous phase of which comprises a polylactic-acid-based material wherein the microvoids are formed by employing relatively smaller size void initiators, including, for example, various inorganic particles such as titanium dioxide.
It is desirable to lessen the number of layers in the support, number of manufacturing processes used to create the layers; and also reduce the amount of materials used in a receiving element to reduce overall manufacturing costs, to reduce issues associated with laminating or adhering materials, and to enable recycling, while maintaining the range of typical properties for ‘imaging media’.